Re: slight tweaks to documentation about runtime pruning

Amit Langote <langote_amit_f8@lab.ntt.co.jp>

From: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
To: Amit Langote <amitlangote09@gmail.com>, David Rowley <david.rowley@2ndquadrant.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-12-14T02:52:03Z
Lists: pgsql-hackers

Attachments

On 2018/12/10 0:57, Amit Langote wrote:
> On Sun, Dec 9, 2018 at 8:13 PM David Rowley
> <david.rowley@2ndquadrant.com> wrote:
>> listp1 was scanned twice (loops=2), listp2 was scanned just once.
>>
>> Now it is true that if the subplan was executed 0 times that it will
>> appear as "(never executed)", but do we really need to explain in this
>> area that "(never executed)" means loops=0?
> 
> Ah, I see what you mean.  So, "(never executed)" is not the only sign
> of of run-time pruning occurring.  The value of loops can be different
> for different subplans / partitions, and it being lower for a given
> subplan means that the subplan has been pruned more number of times.

I updated the patch.  Regarding whether we should mention "(never
executed)", it wouldn't hurt to mention it imho, exactly because it's
shown in the place of showing loops=0.  How about the attached?

Thanks,
Amit

Commits

  1. Clarify runtime pruning in EXPLAIN